1

Understanding Threads

and Fasteners

There are three basic applications for

screw threads:

To hold parts together

To provide for adjustment between parts

To transmit power

2

Screw Thread Terms

Screw Thread Forms

Typical thread forms include:

Sharp-V thread (60 degrees)

American national thread

Unified thread

Unified extra fine thread series

Metric thread

Square thread

Acme thread

3

Screw Thread Forms

Typical thread forms (cont.)

Standard worm thread

Whitworth thread

Knuckle thread

Buttress thread

Screw Thread Forms

4

Thread Pitch

Right-hand and Left-hand Threads

5

Single and Multiple Threads

Single threads are composed of one

ridge and the lead is equal to the pitch

Multiple threads are composed of two or

more ridges running side by side

Single and Multiple Threads

6

Thread Fits

ANSI has established 3 classes of fit:

Class 1 – when clearance between mating

parts is essential

Class 2 – high quality for the bulk of

interchangeable screw thread work

Class 3 – exceptionally high quality

recommended only when high cost of

precision is warranted

Thread Fits

Some specialized metric thread

applications are specified by:

Tolerance grade

Tolerance positions

Class

Length of engagement

7

Methods for Drawing Thread

There are three methods of representing

screw threads on drawings:

Schematic

Simplified

Detailed

Methods for Drawing Thread

8

Methods for Drawing Thread

Methods for Drawing Thread

9

Thread Notes

ASME/ANSI Y 14.6-2001 “Screw Thread Representations” is a standard for representing, specifying, and dimensioning screw threads on drawings These same notes or symbols are used in

correspondence, in records, and in specifications for parts, taps, dies, tools, and gages

Thread Notes

10

Thread Notes

External Thread Symbols

11

Internal Thread Symbols

Detailed Representation

12

Detailed Representation

Use of Phantom Lines

13

Threads in Assembly

Pipe Thread Representation

14

Bolts, Studs, and Screws

Types of Screw Heads

15

Tapped Holes

The bottom of a drilled hole formed by

the point of a twist drill is cone shaped

The thread length is the length of full or

perfect threads

The tap drill depth does not include the cone

point of the drill

Tapped Holes

16

Standard Bolts and Nuts

Standard bolts and nuts have characteristics determined by: Bolt types

Finish

Proportions

Threads

Thread lengths

Bolt lengths

Specifications

In specifying bolts, the following information must be covered in order: Nominal size of bolt body

Thread specification or thread note

Length of bolt

Finish of bolt

Style of head

Name

17

Locknuts and Locking Devices

Standard Cap Screws

18

Standard Machine Screws

Standard Wood Screws

19

Miscellaneous Fasteners

Keys

Keys are used to prevent movement

between shafts and wheels, couplings,

cranks, and similar machine parts

attached to or supported by shafts

20

Keys

Machine Pins

Machine pins include taper pins, straight

pins, dowel pins, clevis pins, and cotter

pins

21

Springs

A spring is a mechanical device

designed to store energy when deflected

and to return the equivalent amount of

energy when released

Springs are classified as:

Helical springs

Flat springs

Helical Springs

Helical springs have three types:

Compression springs

Extension springs

Torsion springs

22

Helical Springs

Compression Springs

23

Compression Springs Required

Information

Extension Springs

24

Extension Springs Required

Information

48Technical Drawing 13th EditionGiesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart

© 2009 Pearson Education, Upper Saddle River, NJ 07458.All Rights Reserved.

Extension Spring

25

Torsion Springs

50Technical Drawing 13th EditionGiesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart

© 2009 Pearson Education, Upper Saddle River, NJ 07458.All Rights Reserved.

Torsion Spring Manufacture

26

Flat

Springs